Fix integration tests generating unwanted chars in input

Signed-off-by: Anthony Chang <antchang@nvidia.com>

integration_tests/src/main/python/string_test.py

@@ -837,16 +837,16 @@ def test_regexp_extract_idx_0():
         conf=_regexp_conf)
 
 def test_word_boundaries():
-    gen = mk_str_gen('([abc]{1,3}[\r\n\t \f]{0,2}[123]){1,5}')
+    gen = StringGen('([abc]{1,3}[\r\n\t \f]{0,2}[123]){1,5}')
     assert_gpu_and_cpu_are_equal_collect(
-            lambda spark: debug_df(unary_op_df(spark, gen).selectExpr('a', 
+            lambda spark: debug_df(unary_op_df(spark, gen).selectExpr(
                 'rlike(a, "\\\\b")',
                 'rlike(a, "\\\\B")',
                 'rlike(a, "\\\\b\\\\B")',
                 'regexp_extract(a, "([a-d]+)\\\\b([e-h]+)", 1)',
                 'regexp_extract(a, "([a-d]+)\\\\B", 1)',
-                'regexp_replace(a, "\\\\b", "")',
-                'regexp_replace(a, "\\\\B", "")',
+                'regexp_replace(a, "\\\\b", "#")',
+                'regexp_replace(a, "\\\\B", "#")',
             )),
         conf=_regexp_conf)